Argon is employed in various processes wherein its chemically inert nature, specific physical properties, and a cost which is low relative to those of other noble gases make its use particularly advantageous. For example, argon is used as a blanketing or purge gas, as a heat transfer medium, for the degassing of reactive impurities in various metal processing operations, and for the atomization of molten metals into fine powder.
While argon is present in air at a much higher concentration than those of the other noble gases, and considerable volumes of argon are available as a byproduct of oxygen and nitrogen production by air separation, the cost of argon still provides significant incentive toward maximizing recycle usage. Therefore, systems have been commercially implemented to conserve argon by means of pressure equalization between vessels, recompression and recycle, generally with particulate separation.
However, the operations in which the argon is utilized often involve periodic exposure of various parts of the system to the surrounding atmosphere. Steps which are conducted at low pressure or vacuum are subjected to potential air infiltration. In addition, materials being processed may degas various impurities. Thus there is a need to purify the spent argon prior to recycle and reuse.
The operation of systems in which argon is employed is frequently batch in nature, resulting in periodic requirements for very high flowrates over relatively short time intervals, and other times when throughput is very low or absent. High pressure receivers, or reliquefaction for compact storage, may be utilized to accommodate these requirements. These conditions make it difficult to match the desired gas contaminant removal to reasonably-sized separation equipment.
Cryogenic distillation and catalytic combustion have both been proposed for the purification of argon in order to promote additional argon conservation. However, both of these methods are costly to implement and to operate. Moreover, the design of a cryogenic distillation system is generally controlled by the maximum instantaneous demand with respect to impurity levels and flowrate. When used in applications such as argon recycle purification, where impurity levels and flows may vary greatly with time, the equipment may then be considerably oversized with respect to the time-averaged requirement. The sizing of catalytic combustion equipment is similarly controlled by the maximum instantaneous requirement.
Accordingly it is an object of this invention to provide an improved method and apparatus for purifying argon.
It is a further object of this invention to provide an improved method and apparatus for purifying argon which can be effectively employed under conditions of wide variations in flows and in impurity concentration levels.
It is yet another object of this invention to provide an improved method and apparatus for purifying argon which is less costly than heretofore available systems.